Conventional complimentary metal oxide semiconductor (CMOS) technology requires gate dielectric layers having higher dielectric constant than SiO2 or SiON. High-k materials such as HfO2 and ZrO2 have been investigated extensively as possible alternatives to SiO2-based options due to their relatively high dielectric constants and large bandgaps. So far, HfO2 has been favored due to its greater stability in contact with Si (e.g., Si substrate or poly-Si electrode), but ZrO2 has been shown to have certain advantages over HfO2, including the possibility of forming the high permittivity and large band gap tetragonal crystallographic form under typical processing conditions used for manufacturing integrated circuits.
In general, HfO2 and ZrO2 have many similar properties and are completely miscible in the solid state. HfO2 and ZrO2 mixtures have been reported to exhibit improved properties over the pure HfO2 and ZrO2 materials, including improved electrical, film growth, and thermal stability characteristics. However, further developments are needed for designing and forming new mixtures of HfO2 and ZrO2 for use as high-k materials in semiconductor devices.
While HfO2 and ZrO2 mixtures have exhibited improved properties, conventional CMOS technology has not successfully utilized HfO2 and ZrO2 mixtures because the combination of Hf and Zr needs to be stabilized. Some crystallographic forms are more desirable than others. However, conventional approaches to the use of mixed Hf and Zr have not resolved how to stabilize a preferred crystallographic form.